US2306425A - Production of ferric sulphate - Google Patents

Description

Dec. 29, 1942. Y J, Q BEVANJ. 2,306,425

PRoDucTloNop FERRC SULPHATEA K Filed Jan. '7, 1939" f Reati/22 Tank Fez (504 /5 INVNTOR VJoh/7 G. Bel/an BY ATTORNEYS acid.I have produced from metallic iron vand sulphur dioxide Patented Dec. 29, 1942 Johnv G. New ,York N... Y.. I

Brothers, New York. N.

Gutlenhfeim copartnership u Application January l This invention relates tofthe production ofv iron kcompounds and has for an object the proa om Y Y? 'zriosasermxaslam I a zomaar. (ci. ssj-1201 vision of an improved` process for'producing ironsulphate. More particularly, Vthe inventionf`contemplates the provision of an' improved process for producing'ferric sulphate. VA furtherobject of the invention is to provide an improved process for utilizing sulphur dioxide,'air, andscrap iron inthe production of ferric sulphate.

Both metallic iron and a` source of sulphur the acid."-The'metallic Y a suitablereagent such asferrlc sulphate or suloxide are readily available in many localities, and

l in producing ferrous iron, the production of ferrie sulphate necessitates Ytreatment :of the ferrous an efficient method for the commercial produc-f` the reagents used sulphate initially formed to cause its further oxi a dation to ferricsulphate, preferably without the formation off. substantial quantities of sulphuric Afound that ferric sulphate canbe withoutthe, need of any reagent', not produced in myaproc'ess, for effecting initial oxidation of the metalliciron.` v f i. Y K

' Ferrie sulphate has found extensive? employment `in sewageV treatment processes. IByy the process ofthe `present invention ferric sulphate may be -made available at smaller'cost than heretofore, thus facilitating the widespread utilization of Water purication processes, for which there isgreat need Vdue to increased concentration of` population and increased production of industrial wastes. The ferric sulphate, moreover, may be produced in aqueousv solutionsubstantially free from sulphuric acid, so that the solution canr be used directly, Ywithout crystallization fromv the solution or addition ofV agents to neutralize acid,

a ablel reagent r capable .ofereacting metallic iron to produceferrous sulphate issulphuricacld,

from which-'iron will displace the hydrogen of iron phur'icacid, or it mayb'e subiectedto the simultaneous action of .several treatment with anaqueous solution containing both ferrie sulphateand sulphuric acid. t

Metallic iron-is easily andcheaply available in theform'of scrap iron, but any source ofunoxidized iron may be utilised inthe processk of the present'in'vention. Sulphurfdioxide maybe obtainedl from commerciall gases, for instance from the gaseousproducts of the roasting of ores containing metallic sulphides, or it may be obtained in any other'mannerrasby treatment of elemental sulphur in a sulphur'burner. Eorthe simultaneous `oxidation of ferrous sulphate? and sulphur dioxide to form ferric sulphate, theoxygen ofthe air is available, but any"gas`,lliquid or be uunzed in this-reaction.

' the-invention, inwhich a portionof the ferric l with metallic u The accompanying .drawing illustrates ldiagrammatically a preferred form ofthe process of sulphate produced' by theac'tionlf sulphur 1di ,iron In this way.

to Aregenerate the reagent-namely, ferrie sul'- in sewage treatment processes requiring control" of acidity.A y ,u u The present invention contemplates broadlyV the treatment of metallic Y, iron with a reagent capable of vreacting with the ironto produce fer'- rous sulphate, and subjecting the ferrous sul'- phate thus producedto the action of sulphur di-r oxide and oxygen Vwith lthe forma-tion of Yferrie sulphate. Ferric Vsulphate itselfpreferably in aqueous solution, is a reagent capable ofreacti'ngY .with metallic iron to produceferrous sulphate, the Ymetallic iron Vbeing oxidized to the ferrous state, andthe ferrie ironfinthefferric sulphate being reduced to the ferrous state. Another suitv5d.uiuuamtefi by the drawing.

phate-which euects ,the initial oxidationofmetallic iron to the ferrous state. The process may be initiated .by treatmentof the metallic iron Awith sulphuric acid, the ferrous sulphate thus formed then reacting withk sulphur dioxide and oxygen to produce theferric sulphate for subsef v quent treatment of metallic iron. 'I'he method of ythe 'invention' may be carried out intermittently by causing contact of batches of the reagents in Vsuitable reaction tanks, or it may beicarried but continuously by Acausing liquid and gaseous-re- 'agentsV to lflo'w, through packed towers.v With Yeither,intermittent or continuous operation, the 'Y Y flow of the materials used in the method ofthe invention in; its preferred form. willfproceed as Thereactionsinvolved v u Y the following chemical equations l Frointhe-se eduations "it will appear that two O1-*FICE mayfbe treatedV with reagentscapable ofY producing ferrous sulphate, l,for instance, by

solidl which contains -or will release oxygenV may mosti-ated by y thirds of the ferrie sulphate produced in accordance with the first reaction is consumed in the oxidation of metallic iron in accordance with the second reaction. Thus to produce 2,000 pounds of ferrc sulphate for removal from the process, 4,000 additional pounds are advantageously formed and returned to the process to replace the ferrous sulphate consumed. The two equations above may be combined into the following single chemical equation, representing the overall method of the invention:

In one batch operation conducted as particularly illustrated in lthe drawing, 625 pounds of scrap iron are treated with a ferrie sulphate solution obtained, for example, from previous batches. The particular solution used in this operation contains about 100 grams of ferrie sulphate per liter of solution. During a retention time of two hours in the reaction vessel 560 pounds (or 90%) of the iron react with 4,000 pounds of ferric sulphate to produce 4,560 pounds of` ferrous sulphate. 'I'he solution containing this ferrous sulphate (and some unreacted ferrie sulphate) is removed to another reaction tank, and 2,390 gallons of water are added to the solution, so that it contains about 27.9 grams of ferrous iron per liter of solution. Then, over a period of 14 hours, 480. pounds of sulphur are caused to combine in a sulphur burner with .part of the oxygen contained in 240,000 cubic feet of air, forming 960 pounds of sulphur dioxide. During the retention time oi 14 hours the gases leaving the sulphur burner, which contain about 2.5% sulphur dioxide and 18.4% uncombined oxygen, are thoroughly mixed with the solution contain- Cil ing ferrous sulphate, causing oxygen and the sulphur` dioxide to dissolve in the solution and react therein with the ferrous sulphate to produce 6,000 pounds of ferric sulphate in 27,300 liters or 7,200 gallons of solution. This resulting solution contains aboutlOO grams per literof ferric sulphate and has a specific gravity of 1.0854. An amount of this solution containing one ton of ferrie sulphate goes to storage as the product of the operation, while the remaining solution is returnedrto the reaction vesselcontaining scrap iron to supplythe ferrie sulphate needed to produce the next batch of ferrous sulphate solution. 'I'he returned solution contains 4,000 pounds of ferric sulphate produced by reaction of ferrous sulphate, sulphur dioxide, and oxygen, and, in addition,`the unreacted ferric sulphate originally` present in the Aferrous sulphate solution removed from the reaction vessel containing scrap iron; the 4,000 pounds of ferrie sulphate iirst mentioned will react with metallic iron to regenerate 4,560 pounds of ferrous sulphate in the next batch operation.

The inventio-n,in a preferred form, utilizes a packed tower containing metallic iron. The iron may be distributed throughout the tower, or the lower portion of the towerV may be packed only with material which does not participate' in the reactions, the iron being confined to the upper oxygen of the air, and ferrous sulphate react to form ferric sulphate. A portion of the ferric sulphate solution leaving the bottom of the tower, large enough to replace the solution previously consumed by reaction with metallic iron, is pumped back to the top for reaction with iron to form more ferrous sulphate. To prevent a. continual increase in the concentration of the solutions owng through the tower, water is added.

Ferric sulphate solution may be continuously removed from the process and water continuously added to the circulating solution until the iron packed in thetower needs replenishing. In a preferred and complete form of the process of the invention, a series of packed towers is used, andthe towers are connected by suitable conduits and pumps, so that solution leaving the bottom of one tower enters the top of the next tower, from the top of which gases are conducted to the bottom of the first-mentioned tower. Thus, ferrie sulphate solutionentering one end portion of the series flows down through each tower in succession to the opposite end portion of the series, while gases containing sulphur dioxide and oxygen, admitted at that opposite end portion of the series, now up through each tower in succession counter-currently to the solution until the unreacted gases leave the series of towers at the first end portion. A portion of the solution leaving the one end portion of the series of towers is returned to the other end portion. Every tower in the series may contain metallic iron, or the ferric sulphate solution, which has undergone reaction with iron to form ferrous sulphate, may pass through one or more towers containing only non-reactive packing material before leaving the series of towers. The mixture of gases, depleted in oxygen' and sulphur dioxide, need not be passed through the tower or towers on the end portion into which the ferrieV sulphate solution is introduced. The ferric sulphate in the solution first reacts with iron to form ferrous sulphate, which then encounters the air and sulphur dioxide, causing the formation of more ferric sulphate than originally entered the series of towers.

Water may be introduced anywhere along'the series of towers, and provision may be made to dilute the solutions in the towersby addingwater at various stages of the Voperation and thusrcontrol the concentration of the solutions. The relative concentration of oxygen and sulphur .dioxide in the gases can,` of course, be controlled bydiluting the sulphur dioxide-containing gas with varying quantities of air. An extra tower may be provided, and the piping and valves may beso arranged that one tower can be substituted for another; in this way, as the iron packed in.

Vto the sulphur burner, so that the gases for reaction with ferrous sulphate containfso much oxygen that only about 14% of the oxygen left after kburning the sulphur is lrequired for the reaction with ferric sulphate and sulphur dioxide.I The gas supplied for this reaction contains sulphurv dioxide and oxygen in a molecular ratioof 0.136 to one.

When themethod `of the invention is carried,v

out commercially, however, it is impractical to convert all the ferrous sulphate formed vinto ferric sulphate and at the same timeavoid the asoman formation of appreciable quantities of sulphuric acid.' The following rtable/will indicate the-dependence of sulphuric acid formation on the ra-y tio of moles of sulphurdioxide to moles kof *oxy-v gen in the gas supplied for reaction with ferrous sulphate, land also the dependence of sulphuric acid formation on the extent to which oxidation of ferrous sulphate to ferric sulphate approaches completion:

Strength Finished product of entering solution, grams ferrous iron, per liter Ratio,

moles SO, t moles Og B0: in Air a Ferric Ferrous iron Grams per liter 28. 4

' the gases.

the solution in the towers does not absorb sulphur dioxide at a faster rate than it absorbs ther oxygeny of `the air. When the solution contains sulphur dioxide in excess of the amount v'equi/va--Y lentfto the oxygengin thefsolution, all of the /sulf phurl dioxide can not react withy oxygen an fer--v rous; sulphate" to" form ferrie4 sulphate; Ieven though the solution contains more than suflicient ferrous sulphate forfthis reaction.` It is then possible that the sulphur dioxide, in solution in excessof oxygen, tends.l to react rinstead with` `1ferricf sulphate ariclwater of the solution, reducing the ferrie iron to the ferrous state and itself f being oxidized to sulphuric acid. To preventthe* formation of sulphuric acid by limiting the absorption of sulphur dioxide relative to oxygen, the gases entering the towers may be diluted with air, or less sulphur may be burned if the source of the sulphur dioxide is a sulphur burner, these procedures tending to decrease the ration of moles of sulphur dioxide to moles of oxygen in When the ratio of moles of sulphur dioxide to moles of oxygen in the gases to be brought into contact with the ferrous sulphate solutionis betweeny about 0.05 and 0.15, the formation of substantial amounts of sulphuric acid will be inhibited, and when in addition a suitable amount of ferrous sulphate remains unoxidized as recommended above, the product will be obtained substantially free of sulphuric acid.

Whether or not the theories advanced to explain the formation of sulphuric acid are correct,

its `formation may be substantially avoided by lowering the ratio of moles of sulphur dioxide to moles of oxygen in the entering gases, or by stopping the reaction before all of the ferrous iron has been converted to the ferrie state, or by resorting to both expedients. Withthis information one skilled in the art to which this invention'appertains will be enabled to produce solutions containing ferric sulphate .but very little ferrous sulphate orsulphuric acid; solutions'containing ferric sulphate, widely varying quantities conditions oxidized sulphurv dioxide will react with j water to form sulphuric acid. Therefore, sulphuric acid production will apparently be. de-l creased by maintaining" an appreciable concentration of ferrous sulphate in the solution leav- 1 ing the reaction tank or the packed towers, as indicated by the upper sets of figures in the above` table. In the` preferred form of the process of. the invention this may-be accomplished by placing more metallic iron in the towers near the gas entrance end portion of the series of towers, or by increasing the rate of flow of, or by decreasing the concentration or amount of, the gases entering the series of towers. It is evident from the above table that, if the 'ferrous sulphate solution is removed' from `contact with the 'gases containing sulphur dioxide and oxygen when about ilve-sixths ofthe iron in the solution have been oxidized ltothe ferric state, substantially complete eliminationcf sulphuric acid from the product may be achieved.

Even though much of the ferrous sulphate remains unoxidized to ferric sulphate in the towers, a, high relative concentration in the entering gases of sulphur dioxide to oxygen will also cause formation of sulphuric acid, as is indicated by the lower sets of gures in the above table. LIn' this way a product is obtained containing substan-y tial quantities of ferric sulphate', ferrous sulphate` and sulphuric acid. It seems that, in order to prevent the formation of sulphuric acid, the air and -sulphurdioxide must be so regulated that of kferrous sulphate, but substantially no sulphuric acid; solutions containing fer'rc sulphate, widely varying quantitiesv of sulphuric acid, but substantially no ferrous sulphate; and" solutions contain ing ferrie sulphate and widely varying quantities Vof both ferrous sulphate andr sulphuric acid.

Whatever the product, a portion of it mayy be utilized for reaction with metallic iron toreplace the ferrous sulphate consumed during the forma-A tion of the desired product. l

,1; The method ofproducing ferrie sulphate which comprises passing an aqueous solution of Lferric sulphate downwardly through a packed tower containing metallic `iron to reduce the iron of the ferric sulphate and oxidize metallic iron with the production of a solution of ferrous sul-l phate Yin the upper portion of the tower, passing gases containing sulphur dioxide and oxygen upwardly through the tower in contact with the downwardly flowing solution gto oxidize the ferrous sulphate contained therein and produce a solution of ferric sulphate in the lowerportion I `ric sulphate solution large enough to replace the solution previously consumed by reaction with 1 lmetallic iron.

of producing ferric sulphatel which comprises introducing an aqueous solution initially containing ferrie sulphate into an end portion of a series of packed towers at least one of which contains metallic iron for downward iiow of the solution through each of the towers in series, introducing gases containing oxygen and sulphur dioxide into the opposite end portion of the series of towersfor upward flow through at least one of the towers in the series in contact with downwardly flowing solution therein, the operation being controlled to effect reduction of ferrie sulphatel initially contained in the solution introduced into the series of towers to ferrous sulphate with simultaneous oxidation of metallic iron to ferrous sulphate, and subsequent oxidation of the ferrous sulphate thus produced to ferric sulphate, withdrawing ferrie sulphatev solution from the gas entrance end portion voi' the series of towers, and returning to the first-mentioned end portion of the series o! towers portions of the withdrawn ferric sulphate solution large enough to replace the solution previously consumed by reactionwith metallic iron.

f JOHN G. BEVAN.

Images